Smoke detection systems can be falsely triggered by exposure to dust. In aspirating smoke detection systems, various analytical solutions have been implemented in order to reduce the dust and thereby avoid a false alarm. In light-scatter-based smoke detection systems, dust discrimination or rejection may be implemented by using time-amplitude analysis (dust tends to produce a spike in the scatter signal which can then be removed) or by using multiple light wavelengths, multiple polarisations, multiple viewing angles, inertial separation, mechanical filtering (e.g through a porous material such as foam), or a combination of the above.
The methods mentioned above act to preferentially remove large particles before they reach the detector or they act to preferentially reduce the signal due to large particles (e.g spike detection and removal). These methods are therefore able to reduce the level of signal due to dust by more than they reduce the level of signal due to smoke. This is because dust contains more large particles relative to smoke.
While dust can be detected via spike detection in the scattered light level there is a concern that this method would not be as effective at high dust levels when the spikes due to dust merge (due to multiple particles simultaneously present in the detection region).
It is therefore an object of the present invention to provide an improved sensing system with dust detection which addresses the abovementioned disadvantages, or at least provides the public with a useful choice over known systems.
Reference to any prior art in the specification is not, and should not be taken as, an acknowledgment or any form of suggestion that this prior art forms part of the common general knowledge in Australia or any other jurisdiction or that this prior art could reasonably be expected to be ascertained, understood and regarded as relevant by a person skilled in the art.